1. Field of the Present Invention
The present invention relates to a method for determining the best GPS position data for a cargo container. More particularly, the present invention provides a method for communicating between multiple GPS enabled devices being transported together and applying analysis to find the exact location of a single unit, container or box.
2. Description of Related Art
Currently, smart container monitoring systems employ GPS transponders to track assets. However, the strength and reliability of the GPS signal can be degraded by many factors. For instance, reliable location data from an automotive GPS may be hampered by metallic features in windshields, such as defrosters or car window tinting films, which can act as a Faraday cage and degrade reception inside the car. Furthermore, man-made electromagnetic interference (EMI) can also disrupt GPS signals. In one well-documented case, it was impossible to receive GPS signals in the entire harbor of Moss Landing, Calif. due to unintentional jamming caused by malfunctioning TV antenna preamplifiers.
Signal degradation can also occur due to intentional jamming. Generally, stronger signals can interfere with GPS receivers when they are within radio range or line of sight. In 2002, a detailed description of how to build a short-range. GPS LI C/A jammer was published in an online magazine. The U.S. government believes that such jammers were used occasionally during the 2001 war in Afghanistan.
There are several techniques which are currently employed to address interference. Receiver Autonomous Integrity Monitoring (RAIM) is included in some receivers, to warn if jamming or another problem is detected. Since 2004, the U.S. military has also deployed their Selective Availability/Anti-Spoofing Module (SAASM) in the Defense Advanced GPS Receiver (DAGR). DAGR detects jamming and maintains its lock on encrypted GPS signals during interference.
Despite various technologies available, there is no reliable solution that enables a shipping container to reliably obtain accurate geo-location data when satellite coverage is limited.